1. Field of the Invention
The present invention relates to the manufacturing of semiconductor devices and the like. More specifically, the present invention relates to bake apparatus for baking a substrate, such as a semiconductor wafer, coated with photoresist.
2. Description of the Related Art
Semiconductor devices are generally manufactured by subjecting a substrate, e.g., a wafer, to ion implantation, deposition, diffusion, photolithography and etching processes. The aim of these processes, especially the photolithography process, is to form a desired pattern on the wafer.
The photolithography process includes coating, exposing and developing processes. In the coating process, the photoresist is dispensed onto the wafer and the wafer is rotated at a high speed so that the wafer is covered with a layer of photoresist to a desired thickness. In the exposure process, the wafer covered with the photoresist and a corresponding mask or reticle are aligned with each other. Then, the layer of photoresist is irradiated with light, such as ultraviolet light, through the mask or reticle so as to transfer a pattern of the mask or reticle to the layer of photoresist. In the developing process, the exposed layer of photoresist is developed to form a desired photoresist pattern. More specifically, either the exposed or non-exposed portion of the layer of photoresist is removed by a developing solution whereby the layer of photoresist is patterned.
In the etching process, a target layer(s) underlying the photoresist pattern is etched using the photoresist pattern as an etch mask. As a result, the target layer(s) is/are patterned.
The photolithography process additionally includes an HMDS(Hexamethyl disilane) process and one or more bake processes. The HMDS process is performed to improve the adhesion of the photoresist to the wafer. A bake process may be performed to remove moisture or an organic solvent from the wafer before the wafer is coated with the photoresist. Also, a bake process may be performed after the wafer has been coated with the photoresist to remove solvent from the photoresist.
A chamber-type of bake apparatus is used to perform the bake process. The bake apparatus includes a chamber, and a hot plate disposed within the chamber. A wafer coated with the photoresist is set on the hot plate and baked at a predetermined temperature within the chamber.
Recently, photolithography has been adapted for use in forming micro patterns on a wafer. In such applications, the extent to which the bake temperature is maintained throughout the bake process, i.e., the bake temperature uniformity, has a large affect on the photolithography or etching process. In other words, maintaining the temperature of the photoresist constant during the bake process is becoming more and more important in the manufacturing of semiconductor devices.
More specifically, the speed at which the temperature of a wafer can be raised to the bake temperature once the wafer is transferred into the chamber of the bake apparatus, and the extent to which the bake temperature can be maintained uniform, are factors that directly affect the production yield of semiconductor devices. Thus, the bake apparatus should be capable of quickly raising the temperature of the wafer and of precisely controlling the temperature of the wafer during the bake process.
FIG. 1 illustrates conventional bake apparatus for baking a typical semiconductor wafer.
The bake apparatus includes a chamber 100, a hot plate 102 installed within the chamber 100, and a buffer plate 108 that is disposed at an upper part of the chamber 100 and has two discharge holes 110 extending therethrough. A wafer 106 is mounted on the hot plate 102, and the hot plate 102 heats the wafer 106 to a predetermined temperature and thereby bakes a photoresist layer on the wafer 106.
Also, the bake apparatus has an air injection passage 104 through which a predetermined quantity of gas (air) is injected into the chamber 100. The gas is pre-heated to predetermined temperature appropriate for the bake process. The buffer plate 108 uniformly disperses the gas within the chamber 100. In addition, the bake apparatus has an exhaust passageway 112 through which the gas is exhausted to the outside via the discharge holes 110 of the buffer plate 108. The buffer plate 108 is circular. The discharge holes 110 have the same diameter and are disposed at the same distance from the center of the circular buffer plate 108.
Also, support pins (not shown) extend from an upper surface of the hot plate 102. These pins support the wafer 106 horizontally above the upper surface of the hot plate 102 so that the hot plate 102 is not in direct contact with the wafer 106.
In the conventional bake apparatus, the gas adjacent the portion of the buffer plate 108 where the discharge holes 110 are present is exhausted quickly, whereas the gas adjacent the other portions of the buffer plate 108 is exhausted slowly. In other words, the gas is not exhausted uniformly from the chamber 100. This causes variations in the thickness of the layer of photoresist which, in turn, results in defects in the pattern formed using the patterned photoresist layer as an etch mask. In particular, a pattern having an unsatisfactory critical dimension (CD) is formed on the wafer.